This invention relates to fan apparatus and more particularly to fan apparatus having adjustable pitch blades.
The movement of fluids, notably air, is the principal application for a fan. Fans are therefore commonly used in systems requiring the movement of air for ventilation, heat transfer, moisture transportation and the like.
An agricultural application in which fan apparatus is beneficially used involves drying harvested grain crops and the like to improve the quality thereof and to correspondingly enhance its value. For example if corn is properly dried it is worth more since it may then be used in specialty markets such as prepared cereals.
The recognition of this fact has lead to various methods and apparatus for suitably drying grain products. One commonly used method is batch drying which utilizes an external heat source and a high speed fan in order to dry the grain expeditiously in the least possible time. The problem with drying grain using artificial heat sources where thermal output is high is that the dried grain is often damaged due to prolonged exposure to high temperatures. Thus, temperatures of from 110.degree. to 200.degree. F. cracks the skins of kernels making corn that is dried under these conditions unsuitable for running through special rollers which extract the delicate germ needed for processed food use.
A preferred method now in use dries corn naturally without incurring enormous costs involving vast amounts of heat energy. Storage bins, which are more or less conventional in structure, include an opening in a closed top of the bin through which air is drawn and conducted through the stored grain to the bottom of the bin where the air and its accumulated moisture is exhausted. Depending on the humidity content of the atmosphere, the air may be directly drawn into the bin or it may be slightly heated to control its moisture content. This may require warming the air slightly, probably not more than 5.degree. F. higher than the ambient air temperature. Where the bin temperature is from 2.degree. to 4.degree. F. warmer than outside air, spoilage of the stored grain is reduced since fewer bacteria are formed.
Under such mild operating conditions, a reliable fan system is required since long periods of operation ensue. Drying time usually runs from harvest of the grain to the following January and February when the grain is normally sold and trucked away. Furthermore, the fan apparatus must be efficient in its operation in order to conserve electrical energy over the long period that it is operated, and it must be capable of matching the output to intake of air, particularly since loaded bins will vary in their characteristics due to the type of grain stored.
In order to maximize the efficiency of any fan apparatus, the fan blade portion thereof must be suitably coupled to its source of air to minimize slippage and to maximize air throughput. One way in which this may be performed includes a fan blade assembly having adjustable pitch blades. An alternative approach is to provide fan apparatus having variable drive means.
In the former case, ancillary problems arise which must be overcome if reliable apparatus is to be produced. Problems that are frequently encountered include blades that disengage from a hub and fly off due to strong centrifugal forces, irregular settings of individual blades which cause an unbalanced condition leading to excessive vibrations and resulting damage therefrom, and blades that are individually set which requires considerable time for accurate, uniform setting of all blades.